Method for safe filling with carbon nanotubes, filling system and industrial plant employing this method

ABSTRACT

The invention relates to a method for filling a receptacle ( 200 ) with carbon nanotubes from another receptacle ( 106 ) whereby the CNTs are passed from one receptacle to the other by means of a coupling ( 300 ) comprising a double-valve device ( 30 ), each valve being coupled to one of the receptacles, the valves ( 31, 32 ) closing independently and tightly and being openable only when they are coupled to one another.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/361,652, filed on Jan. 29, 2009, which claims priority to FR08.50674, filed Feb. 4, 2008, the entireties of which applications areincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an industrial method for safely filling areceptacle with carbon nanotubes (CNT) from another receptacle. Theinvention also relates to a filling system employing the method. Theinvention also relates to a plant for the safe packaging of carbonnanotubes, which is equipped with a filling system according to theinvention.

Carbon nanotubes (CNT) are particles of a diameter ranging between 0.4nm and 50 nm and of a length in excess of 100 times their diameter. CNTsform bundles such that they exist in the form of a powder of a range ofparticle sizes in which the mean diameter of the particles is about 400microns.

The expansion in activity relating to CNTs has lead the applicant, intheir capacity as a CNT manufacturer, to handle significant quantitiesof CNT powder and to seek solutions to allow CNTs to be packaged intocontainers and transported between reactor and storage hopper. However,handling CNTs and designing systems for packaging and transporting themcould potentially raise issues of environmental and personal safety, 20even though to date the risks involved if CNT powder were to be releasedinto the air, even at low doses, are not known.

What has happened is that the applicant has run into difficultiesparticularly when filling a receptacle with CNTs from anotherreceptacle. Receptacle-filling operations have to be performed once anindustrial plant for packaging CNTs into containers has been 25designed.

What has happened is that the applicant has had to solve the problem oftransferring CNTs on an industrial scale without knowing what impactCNTs might have on man and the environment. In order to solve thisproblem, the applicant has chosen a solution which provides the maximumlevel of safety with respect to the environment and 30 which iscompatible with use on an industrial scale.

In this context, the applicant has chosen to take a precautionaryapproach and has sought a solution such as to afford a maximum level ofsafety when transferring CNTs from one receptacle to another receptaclethrough a mechanical connection positioned between the two receptacles.The applicant has, in particular, sought a solution that affords maximumsafety for the operations of filling a CNT packaging receptacle withCNTs from a storage receptacle in a way that is compatible with anindustrial process.

In this same approach, the applicant has sought a solution that presentsa maximum level of safety throughout an industrial plant developed totransport CNT powder from the reactor in which the CNTs are manufacturedas far as the point where they are packaged into containers.

To these ends, the applicant has developed a safe filling method wherebythe coupling between a receptacle containing the CNTs and a receptacleintended to receive the CNTs is achieved by means of a safe double-valvedevice.

A double-valve device provides the tightest possible seal and thehighest level of safety with respect to the environment during transferand also afterwards because those parts of the valves that are exposedto the open air do not become soiled during transfer.

PRIOR ART

Document EP 1 468 917 describes a device for transferring powder,granules, paste, liquid or gas from one container to another container.That transfer device is made up of a cone valve that closes off theopening of one container, of a drive mechanism for moving the conevalve; of a shut-off head positioned on the other container and of amechanism allowing the head to be moved inside the container under thethrust of the cone valve, this same mechanism ensuring that the shut-offhead returns to its initial position when there is no driving thrust.

The cone valve is moved by the drive mechanism of the hydraulic,electrical or pneumatic cylinder type housed in one container.

The head is coupled to the return mechanism housed in the othercontainer.

The drive mechanism that drives the valve is housed inside thecontainer. It is therefore necessary to adapt the container in order toallow this mechanism to be controlled from the outside.

The device described in that document does not deal with the transfer ofcarbon nanotubes. In any event, that transfer device is unsuited tocarbon nanotubes because, being inside the container, the drivemechanism that drives the valve is in contact with the powder that is tobe transferred. There is therefore a risk of soiling and ofmalfunctioning, which risk increases as the powder that is to betransferred becomes more fine, and nanoparticles such as carbonnanotubes are extremely fine.

Further, that device is ill suited to an industrial method for fillingwith carbon nanotubes because the device entails containers that arespecially adapted to take external controls so that the movement of thecone valve can be actuated.

Aside from these disadvantages, the transfer device made up of this typeof valve is complex and bulky because it contains a valve drivemechanism and a head return mechanism each moving in the container thathouses them and along the longitudinal axis of this container.

SUMMARY OF THE INVENTION

Thus, in order to provide the maximum level of safety for transferringcarbon nanotubes and to afford an industrial solution to the transfer ofCNTs from one site to another, the applicant has chosen to fit thecontainers with double-valve devices such as, for example, a device ofthe “Buck®” or “Glatt®” type. These devices are also known by the nameof butterfly valves. These are compact devices in the form of two flatcylindrical elements that are very compact and seal very tightly. Eachelement constitutes one valve, one being known as the active valve andthe other as the passive valve.

Hitherto, double-valve devices of the “Buck®” or “Glatt®” type have beenused to handle small volumes of powders of a particle size greater indiameter than CNTs, in pharmaceutical laboratories.

Such devices comprise an active first valve and a passive valve. Theopening control is on the periphery of the active valve of the device.The double-valve device can be opened only when the two valves arecoupled to one another. The opening control is locked when there is nocoupling. The passage between two receptacles connected to one anotherby this type of valve is opened and closed by shutters that face oneanother and pivot about a diametral axis under the action of the openingcontrol. The faces of the shutters that are in contact with the productscontained in the receptacles are never in contact with the outside.Thus, after the two valves have been disconnected, no product (powder orthe like) is present on the external faces of the shutters. This thenprotects the environment while products are being transferred and evenafterwards.

A more particular subject of the invention is an industrial method forfilling a receptacle with carbon nanotubes from another receptaclewhereby the CNTs are passed from one receptacle to the other by means ofa coupling comprising a double-valve device, each of the valves beingcoupled to one of the receptacles, the said valves closing independentlyand tightly and being openable only when they are coupled to oneanother, the said device being a double-valve device of the butterflyvalve type.

When the filling method is applied to the metering of CNTs, the CNTs areto transferred from a container to a metering device, and the methodthen consists in connecting the valve known as the active valve to thecontainer and the other valve known as the passive valve to the meteringdevice.

When the filling method is being applied to the packaging of CNTs incontainers from a storage hopper, the method consists in coupling avalve known as the active valve to the outlet line of the hopper and theother valve known as the passive valve to the container.

The invention also relates to an industrial system for filling areceptacle with carbon nanotubes from another receptacle, the system tothis end comprising a means of coupling between the two receptacles,comprising a double-valve device, it being possible for a first valve tobe coupled to one of the receptacles, it being possible for the othervalve to be coupled to the other receptacle, each of the valves closingindependently and tightly once they have been fitted to the receptacles,it being possible for the two valves to be coupled to one another, thiscoupling allowing them to be opened, the said device being adouble-valve device of the butterfly valve type.

At least one valve of the double-valve device is active, that is to saythat it comprises an opening control. The second valve is a passivevalve.

The double-valve device is flat and compact and has shutters that faceone another and pivot about a diametral axis under the action of anopening control on the external periphery of the active valve.

The filling system may comprise an adapter to adapt the opening diameterof the container to the diameter of the valve. An adapter may be fixedto the opening of each container to allow coupling with the valves.

The invention applies to any receptacle equipped with a valve of adouble-valve device to allow CNTs to be transferred from one receptacleto the other or allow one receptacle to be filled with CNTs from theother.

Receptacles of the storage receptacle type are coupled to the activevalve of the double-valve device.

Receptacles in which the CNTs are packaged or other transfer receptaclesare coupled to the passive valve of the device, it being possible forthis valve to be, for example, connected directly to the opening of thereceptacle.

The invention also relates to an industrial plant for packaging CNTsinto containers, the said plant being equipped with a carbon nanotubesfilling system according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a CNT filling system for implementing the methodin a first application that involves transferring CNTs from a firstreceptacle to another receptacle,

FIG. 2 is a diagram of an industrial plant for packaging CNTs intocontainers, using a CNT filling system that implements the method,

FIGS. 3A and 3B are cross sections on AA of the device 30 of FIGS. 4Aand 4B, respectively, in the uncoupled then in the coupled position;FIGS. 3C and 3D are cross sections on BB of this same device;

FIG. 5 is a diagram of an industrial plant for packaging CNTs with apneumatic conveyor line between the reactor 100 and the packaging stage.

DETAILED DESCRIPTION OF THE INVENTION

Large-scale handling of CNTs has lead the applicant to develop anindustrial plant covering the phases from manufacture, that is to sayfrom the reactor in which the CNTs are formed, to the packaging of CNTsin containers, the sizes of which vary from 201 to 20001 depending onthe anticipated end-use.

The present invention falls into the context of this development andapplies to the transfer of CNTs from one receptacle to another when onereceptacle needs to be mechanically coupled to another, either directlyor via an outlet line, whether this be a packaging receptacle or anyother receptacle, for example a metering receptacle.

The description given hereafter illustrates the use of the methodaccording to the invention in two applications and the system used forimplementing the method.

In a first application illustrated by the diagram that is FIG. 1, themethod and the implementation system allow CNTs to be transferred to areceptacle 20 from another receptacle 10 containing CNTs. The receptacle20 into which the CNTs are transferred, may for example, be a meteringdevice. The receptacle 20 is a storage container.

The coupling 300 between the two receptacles 10, 20 is achieved via thedouble-valve device 30, a valve 31 and a valve 32 being connected toeach opening of the two receptacles.

A suction device 50 coupled to the device 30 may be provided in order toextract any CNT powder residue from the connection.

For transporting the CNTs there is no need to use shuttle containers,that is to say containers the opening of which has the same diameter asthat of the double valves. Containers of standard diameter may be used.To do that, the lid of the container is removed. Provision is then madefor the transfer device to be fitted with a diameter adapter, referenced33 in FIG. 1. This is because the diameters of standard containers aregreater than those of the double valves. The adapter 33 is cone-shapedsuch that one of its openings is attached to the container in place ofthe lid, the other opening being fixed to a valve 31 and/or 32.

The CNT filling method in the case of a second application which is thatof packaging CNTs in containers will now be described.

In a first practical exemplary embodiment illustrated by the diagramthat is FIG. 2, packaging is performed without transporting the CNTs,these being transferred from a storage hopper 103 in which the CNTpowder is held, into containers 200. The mechanical coupling between theoutlet of the hopper 103 and the opening of the container 200 isachieved by means of a double-valve device 30 of the “Buck®” or “Glatt®”butterfly-valve type, marketed by the company of the same name. Thisdevice may have an adapter 33 or adapting the diameter fitted to thecontainer 200 if the diameter thereof is not the same as that of thevalve 32.

The elements that make up the industrial plant I1 from the reactor 100as far as the packaging station are:

-   -   a cooler 101    -   a screen 102    -   a storage hopper 103    -   valves 301, 302    -   a filling system 300 for packaging, comprising a double-valve        device 30.

In order to obtain a very high quality powder with no coke present, thelargest particles are removed. To this end, a screen 102 is positionedafter the cooler in order to separate out the large particles. Thisscreen 102 must be completely sealed and allow no contact whateverbetween the operator and the CNT powder, and for example may be acompact screen by the company RITEC. The cut-off of the screen is 2 mmwith the screen diameter of 400 mm for a filtration area of 0.1 m². Thistool gives continuous screening of the powder at a high flow rate, theadvantage of this equipment being its lateral motors which allow forgreater screening performance.

The hopper 103 is coupled to the outlet of the screen. The hopper ispreferably pyramid-shaped and made of stainless steel with, in thisparticular exemplary embodiment, a capacity of 350 1.

The mechanical coupling 300 allows for safe filling between the CNTinlet from the hopper and the opening of the container 200 by virtue ofthe butterfly-type double-valve device 30.

The CNTs from the hopper 103 may, in an alternative version not depictedin this diagram, pass through a control valve. The active valve 31 ofthe device 30 would then be coupled to this control valve.

The packaging container 200 is coupled to the passive valve 32 of thedevice 30.

The butterfly-type double-valve device of the “BUCK” type for examplemakes it possible to avoid any contact between the powder and theoutside, and the CNT powder can thus be transferred in complete safety.By virtue of the technology of this type of valve, the way in which theCNT powder is transferred is highly contained and free of dust. Thedesign of this valve prevents any possibility of the CNT powder leakingto and contaminating the outside.

In this example, the passive valve 32 of the device is connected to theopening of the packaging containers 200 while the active valve 31 isconnected to the outlet of the storage hopper.

Reference may be made to the diagrams that are FIGS. 3A to 3D and 4A to4D in order to understand how the double-valve device describedhereinafter works.

When the passive valve 32 on a receptacle 20 or container 200 is coupledto the active valve 31 receiving the CNTs from another receptacle 10(FIG. 1) or from the hopper 103 (FIG. 2), the two external faces of theshutters 34 and 35 of the valves are pressed together, preventing anyCNT powder from soiling these faces. Thus, when the valves 31, 32 areseparated, the faces of the shutters 34, 35 find themselves in contactwith the outside but have not been soiled with the powder. Further, thecoupling of the two valves 31, 32 unlocks the opening control 36 and theshutters can then pivot under the action of the control. The control maybe automatic or manual.

The opening of the double valve then allows CNT powder to flow withoutany external leak.

In a second example illustrated by the diagram that is FIG. 5, packagingis performed after transport. In this case, the plant I2 comprises acircuit conveying the CNTs from the reactor 100 in which they weremanufactured to a remote storage hopper 106 (for example one situated inanother building or on a different floor).

The type of transport chosen is pneumatic conveying in the dense phasein order to preserve the quality of the CNT powder and avoid thegeneration of fine particles. The gas used is air.

In order to make the transportation completely safe, an operation hasbeen chosen in which there is a vacuum in the circuit such that, in theevent of a leak, no CNT powder can be discharged into the atmosphere.

The elements that make up the industrial plant from the reactor 100 asfar as the packaging stage are:

-   -   a reactor (100) in which the CNTs are formed,    -   a cooler (101),    -   an airlock (120),    -   a pneumatic conveyor (400),    -   a vacuum chamber (105) with air filtration (108),    -   an in-line screen (102),    -   the storage hopper (106),    -   a metering valve (104),    -   an air filter (107),    -   a filling system 300 for packaging using a butterfly-type        double-valve device (device with safety valves).

The airlock 120 allows CNT powder produced by the reactor 100 to berecovered and this powder to be inerted by alternating vacuum withnitrogen in order to eliminate any trace of ethylene and, above all, ofhydrogen, before pneumatic conveying is performed.

This airlock 120 may also be fitted with a pressurizer so that it can,if appropriate, operate with blowback.

The presence of hydrogen may prove hazardous in the event of leakage andcontact with the air. The carbon nanotubes will not be transported untilan in-line analyser positioned at the exit of the air lock 120 (beforethe CNTs are transported) has checked the ethylene concentration. Itwill be assumed that if no further ethylene is present then the hydrogenwill also have disappeared.

In order to obtain a very high quality powder with no coke present, thelargest particles are eliminated. To do this, an in-line screen 102 ispositioned in the transport circuit 400 after the vacuum chamber 105 inorder to separate out the large particles. This screen 102 must becompletely sealed and allow no contact whatever between the operator andthe CNT powder, and for example may be a compact screen by the companyRITEC. The cut-off of the screen is 2 mm with a screen diameter of 400mm for a filtration area of 0.1 m². This tool gives continuous screeningof the powder at a high flow rate, the advantage of this equipment beingthe result of the lateral motors which allow for greater screeningperformance.

The hopper 106 is preferably pyramid-shaped and made of stainless steelwith, in this particular exemplary embodiment, a capacity of 350 1.

A weighing device, not depicted, may make it possible at any moment todetermine the amount of CNTs produced in the reactor 100.

The air conveyed with the CNT powder is sent to an air filtration device107 equipped with very high efficiency filters such as HEPA filters H14.An HEPA filter has the ability to retain particles of a diameter of 0.3μm in the air with an efficiency of 99.995%.

The filling system for packaging CNTs offers the possibility ofproviding various different volumes (small volumes 11 to 101, bigvolumes 601 to 2001 until 1 m³ (in weight from 100 g to 100 kg andmore)) of carbon nanotubes and of operating in complete safety withouthandling the powder.

The mechanical coupling 300 between the inlet of CNTs from the hopperand the opening of the container is achieved by means of abutterfly-type double-valve device 30 (of the “Buck®” or “Glatt®” type).

The CNTs from the hopper pass first of all through the control valve104. The active valve 31 of the device 30 is coupled to this controlvalve 104.

With a view to avoiding excessive bulk, the control valve 104 comprisesa metering device of the DOSIMAT© type. This valve has a cross sectionDN 150 and consists of a circular disc set in motion by a cylinderwhich, when pivoting about an axis, opens the way to a greater or lesserflow of product through a crescent-shaped opening that can vary frombeing completely closed to wide open.

Provision may also be made for the receiving container to be emptiedafter transport into a receiving hopper with which the plant that willuse the CNTs is equipped. When this is the case, the receiving hopper isfitted with an active valve in order to allow the transfer to beperformed in complete safety.

The industrial plant that has just been described allows CNT powder tobe packaged in complete safety, this safety being afforded at the timeof packaging into containers and also throughout the transport line fromthe reactor as far as the safe coupling device 30.

What is claimed:
 1. A system for filling a second receptacle with carbon nanotubes from a first receptacle, said system comprising a means of coupling the two receptacles, comprising a double-valve device comprising a first valve, of the butterfly valve type, and a second valve, of the butterfly valve type, said first valve removably coupled to said first receptacles and said second valve removably coupled to said second receptacle, each of the valves closing independently and tightly upon coupling to said receptacles, and a means for coupling said first valve to said second valve whereby said valves operate in tandem when coupled and being opened.
 2. The system according to claim 1, wherein said first valve of the double-valve device is an active valve, comprising an opening control, and said second valve is a passive valve.
 3. The system according to claim 2, wherein said double-valve device is flat and compact and has shutters that face one another and pivot about a diametral axis under the action of means for opening said double-valve device mounted on the external periphery of said active valve.
 4. The system according to claim 1, further comprising an adapter to adapt the diameter of the first receptacle to the diameter of the double-valve device.
 5. The system according to claim 1, wherein the system is fitted with a valve of a double-valve device of the butterfly valve type, which valve is able to be coupled to another valve of the device in order to transfer carbon nanotubes (CNTs) from one receptacle to the other or fill one receptacle with CNTs from another.
 6. The system according to claim 1, wherein said first receptacle comprises a carbon nanotube storage receptacle coupled to said first valve of said double-valve device.
 7. The system according to claim 1, wherein said second receptacle comprises a package from carbon nanotubes coupled to said second valve of said double-valve device.
 8. An industrial packaging plant, comprising: a system for filling according to claim 1, a reactor in which carbon nanotubes (CNTs) are formed, a cooler, an airlock, a pneumatic conveyor, a vacuum chamber with air filtration, an in-line screen, a storage hopper, a metering valve, and an air filter. 